My, what big eyes you have. All the better to see you with? A comparison of eye diameter and maximum gape between native and non-native fishes from the southwestern United States

Authors: Clinton J. Moran, Tammy L. Knecht, Alice C. Gibb

Year: 2012 (xliv)

Abstract

Eye size in predators ranging from mammals to fishes has been associated with visual capabilities. Lager eyes allow more photons to enter the eye per solid angle of image. Many southwest cyprinids have evolved in turbid environments, so turbid that vision perhaps played a reduced role in their sensory systems than what is required in today’s less turbid environments. Thus we observe small beady eyes in most of the cyprinids across the southwest. We photographed several members of the southwestern Cyprinidae as well as many introduced piscivores. Using imaging programs we digitized eye diameter, maximum gape, and standard length. With these measurements we compared both within the natives and between natives and non-natives. Within the native Cyprinids there was comparatively little variability in eye size relative to standard length. However, when non-native piscivores were introduced to the comparison it was clear that native Cyprinids have significantly smaller eyes than non-native predators. When comparing native cyprinids to non-natives maximum gape was also typically much larger in non-native piscivores. Consistently, the largest maximum gape per unit of standard length was seen in the Centrarchidae. These results have significant implications for the current and future state of southwestern Cyprinids. Having smaller eyes relative to a competitor or predator has drastic survival and competitive disadvantages. Predation on the Cyprinidae, at all life history stages, and higher competitor fitness play a significant role in the decline of the southwest Cyprinidae.